Browsing by Author "Chang, Chih-Min"

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A 95-dBA DR Digital Audio Class-D Amplifier Using a Calibrated Digital-to-Pulse Converter
(2017-05-01)
Chang, Chih-Min
;
Wu, Jieh-Tsorng
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電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A digital class-D amplifier (CDA) converts an audio digital stream into sound directly and power-efficiently. It first encodes the pulse-code-modulated audio input into a digital pulse-width-modulated (PWM) signal. It needs a digital-to-pulse converter (DPC) to translate this digital PWM signal into a series of analog binary pulses accurately. We report a 5-3 segmented DPC that includes both a counter and a delay line for pulse width conversion. The timing skews along the delay line are detected using a zero-crossing detection scheme and corrected in the digital domain. This calibration can operate continuously in the background. A digital CDA prototype was fabricated using a 65-nm CMOS technology. It includes the aforementioned PWM modulator and DPC. It also integrated an open-loop switching driver to deliver the DPC's output to a speaker. This digital CDA consumes 875 mu W under a 1-V supply when the input is zero and no output power is transferred to the external load. It can deliver 13.3 mW to a 32 Omega resistive load in the H-bridge topology with 89% power efficiency. For a 1-kHz sine-wave input, it achieves 95 dBA dynamic range, 93.6 dBA peak SNR, 86.4 dBA peak SNDR, and 0.006% THD at -2-dBFS input level. The core area of the chip is 0.87 x 0.5 mm(2).
A Computationally-Efficient PWM Technique for Digital Class-D Amplifiers
(2016)
Chang, Chih-Min
;
Wu, Jieh-Tsorng
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We describe a technique that digitally converts a pulse-code-modulated (PCM) signal to a pulse-width-modulation (PWM) signal. This technique is based on the naturally sampled PWM emulation scheme. Its computation is simplified by using empirical models. It provides sufficient accuracy with minimal computation. At 384 kHz sampling rate, the proposed technique can convert a sine wave to a PWM signal and achieve better than 92 dB total harmonic distortion (THD) for a sine wave frequency up to 20 kHz and a sine wave amplitude up to 90% of the full range.
Evolutionary information hidden in a single protein structure
(2012-06-01)
Shih, Chien-Hua
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Chang, Chih-Min
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Lin, Yeong-Shin
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Lo, Wei-Cheng
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Hwang, Jenn-Kang
The knowledge of conserved sequences in proteins is valuable in identifying functionally or structurally important residues. Generating the conservation profile of a sequence requires aligning families of homologous sequences and having knowledge of their evolutionary relationships. Here, we report that the conservation profile at the residue level can be quantitatively derived from a single protein structure with only backbone information. We found that the reciprocal packing density profiles of protein structures closely resemble their sequence conservation profiles. For a set of 554 nonhomologous enzymes, 74% (408/554) of the proteins have a correlation coefficient > 0.5 between these two profiles. Our results indicate that the three-dimensional structure, instead of being a mere scaffold for positioning amino acid residues, exerts such strong evolutionary constraints on the residues of the protein that its profile of sequence conservation essentially reflects that of its structural characteristics. Proteins 2012;. (c) 2012 Wiley Periodicals, Inc.
Internal energy of HCl upon photolysis of 2-chloropropene at 193 nm investigated with time-resolved Fourier-transform spectroscopy and quasiclassical trajectories
(2008-12-14)
Chang, Chih-Min
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Huang, Yu-Hsuan
;
Liu, Suet-Yi
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Lee, Yuan-Pern
;
Pombar-Perez, Marta
Following photodissociation of 2-chloropropene (H(2)CCClCH(3)) at 193 nm, vibration-rotationally resolved emission spectra of HCl (upsilon <= 6) in the spectral region of 1900-2900 cm(-1) were recorded with a step-scan time-resolved Fourier-transform spectrometer. All vibrational levels show a small low-J component corresponding to similar to 400 K and a major high-J component corresponding to 7100-18 700 K with average rotational energy of 39 +/-(11)(3) kJ mol(-1). The vibrational population of HCl is inverted at upsilon=2, and the average vibrational energy is 86 +/- 5 kJ mol(-1). Two possible channels of molecular elimination producing HCl+propyne or HCl+allene cannot be distinguished positively based on the observed internal energy distribution of HCl. The observed rotational distributions fit qualitatively with the distributions of both channels obtained with quasiclassical trajectories (QCTs), but the QCT calculations predict negligible populations for states at small J. The observed vibrational distribution agrees satisfactorily with the total QCT distribution obtained as a weighted sum of contributions from both four-center elimination channels. Internal energy distributions of HCl from 2-chloropropene and vinyl chloride are compared.
On the relationship between the sequence conservation and the packing density profiles of the protein complexes
(2013-07-01)
Chang, Chih-Min
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Huang, Yu-Wen
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Shih, Chien-Hua
;
Hwang, Jenn-Kang
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生物資訊及系統生物研究所
We have recently showed that the weighted contact number profiles (or the packing density profiles) of proteins are well correlated with those of the corresponding sequence conservation profiles. The results suggest that a protein structure may contain sufficient information about sequence conservation comparable to that derived from multiple homologous sequences. However, there are ambiguities concerning how to compute the packing density of the subunit of a protein complex. For the subunits of a complex, there are different ways to compute its packing density - one including the packing contributions of the other subunits and the other one excluding their contributions. Here we selected two sets of enzyme complexes. Set A contains complexes with the active sites comprising residues from multiple subunits, while set B contains those with the active sites residing on single subunits. In Set A, if the packing density profile of a subunit is computed considering the contributions of the other subunits of the complex, it will agree better with the sequence conservation profile. But in Set B the situations are reversed. The results may be due to the stronger functional and structural constraints on the evolution processes on the complexes of Set A than those of Set B to maintain the enzymatic functions of the complexes. The comparison of the packing density and the sequence conservation profiles may provide a simple yet potentially useful way to understanding the structural and evolutionary couplings between the subunits of protein complexes. Proteins 2013; 81:1192-1199. (c) 2013 Wiley Periodicals, Inc.
Sequence Conservation, Radial Distance and Packing Density in Spherical Viral Capsids
(2015-07-01)
Chang, Chih-Min
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Huang, Yu-Wen
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Lee, Chi-Wen
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Huang, Tsun-Tsao
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Shih, Chung-Shiuan
The conservation level of a residue is a useful measure about the importance of that residue in protein structure and function. Much information about sequence conservation comes from aligning homologous sequences. Profiles showing the variation of the conservation level along the sequence are usually interpreted in evolutionary terms and dictated by site similarities of a proper set of homologous sequences. Here, we report that, of the viral icosahedral capsids, the sequence conservation profile can be determined by variations in the distances between residues and the centroid of the capsid - with a direct inverse proportionality between the conservation level and the centroid distance - as well as by the spatial variations in local packing density. Examining both the centroid and the packing density models against a dataset of 51 crystal structures of nonhomologous icosahedral capsids, we found that many global patterns and minor features derived from the viral structures are consistent with those present in the sequence conservation profiles. The quantitative link between the level of conservation and structural features like centroid-distance or packing density allows us to look at residue conservation from a structural viewpoint as well as from an evolutionary viewpoint.
The conservation profile of a protein bears the imprint of the molecule that is evolutionarily coupled to the protein
(2015-08-01)
Huang, Yu-Wen
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Chang, Chih-Min
;
Lee, Chi-Wen
;
Hwang, Jenn-Kang
;
生物資訊及系統生物研究所
The conservation profile of a protein is a curve of the conservation levels of amino acids along the sequence. Biologists are usually more interested in individual points on the curve (namely, the conserved amino acids) than the overall shape of the curve. Here, we show that the conservation curves of proteins bear the imprints of molecules that are evolutionarily coupled to the proteins. Our method is based on recent studies that a sequence conservation profile is quantitatively linked to its structural packing profile. We find that the conservation profiles of nucleic acid (NA) binding proteins are better correlated with the packing profiles of the protein-NA complexes than those of the proteins alone. This indicates that a nucleic acid binding protein evolves to accommodate the nucleic acid in such a way that the residues involved in binding have their conservation levels closely coupled with the specific nucleotides. Proteins 2015; 83:1407-1413. (c) 2015 Wiley Periodicals, Inc.